1. Field of the Invention
This invention relates generally to shaker plates and, more specifically, to a method making a shaker plate which exactly and precisely fits the outline of a sand core which has ridge of flash sand that must be removed.
2. Description of the Prior Art
In today's foundries, a typical high speed molding machine can cycle every 15 to 20 seconds. Many of the molds used in these machines require identical sand cores. Typically, the sand cores are made with curing sands which are placed in metal core boxes that are heated to about 500.degree. F. above room temperature. This firing produces a rigid but somewhat fragile sand core which can be used with the molding machines. After removing the sand cores from the metal core boxes, the sand cores are usually not ready to be placed into a mold as the sand cores require mechanical cleaning by removing the flashsand located at the joint where the two halves of the metal core boxes join. The sand web or flash is the result of the fine grains of sand collecting at the joint of the core box and then hardening as a thin ridge or web during the curing stage of the sand core.
In the past, the cleaning or deburring has been done by hand by core room personnel who use either a file or a wire to scrape off the sand ridge. If this excess flash sand is not completely removed from the entire core, the casting made in the mold which uses this sand core could be ruined because of the mis-shaping of the final cast article.
Another prior art process is to make a metal shaker plate that passes over the sand core and removes the flash by the vibration of the plate.
The present invention is to a process of manufacturing a shaker plate which precisely and exactly passes over the sand core so that it can be used to strip off any unwanted ridges of sand on the sand core. In actual operation, the sand core is passed through a vibrating flat steel plate called a "stripper plate." This stripper plate has a two-dimensional opening which is substantially identical to the sand core. The vibration of the plate cuts or shears off the unwanted web of fine sand grains on the sand core. The use of a shaker plate reduces the time involved in removing the web of sand along the flash joint and allows for automated finishing of sand cores in a matter of a few seconds rather than minutes.
The problem involved with this process is how to make a shaker plate which has the same dimensions as the sand core. The reason it is difficult to do so is the metal core box pattern and the sand core have a different dimensioneven though the sand core is made in the metal core box. The reason the sand core is larger than the metal core box is that to make the sand core, the metal core box temperature is increased by about 500.degree. F. This produces a thermal expansion of the metal core box which results in the sand core curing and hardening in the expanded metal core box. As a result, the sand core is substantially larger than the metal core box when both are at room temperature. Consequently, it is difficult to use the room temperature undersized metal core box as a pattern for making a shaker plate. The present invention overcomes this difficulty through a process of casting which compensates for the undersized metal core box.